Device for radiation measurements on material webs

ABSTRACT

Apparatus is disclosed for the measurement of a variable parameter at different points distributed across the width of a web of material travelling lengthwise relative to the apparatus. The apparatus includes a first set of &#39;&#39;&#39;&#39;light tubes&#39;&#39;&#39;&#39; fixed in relation to said apparatus and extending from a light source transversely of the web of material with their output ends spaced across the width of the web of material. A second set of &#39;&#39;&#39;&#39;light tubes&#39;&#39;&#39;&#39; also is fixed in relation to said apparatus and extends from light sensitive means transversely of the web material with their input ends spaced across the width of the web of material. The input ends are respectively associated with corresponding light output ends of the light tubes of the first set.

United States Paten n91 Tirkkonen et a1.

[ DEVICE FOR RADIATION MEASUREMENTS ON MATERIAL WEBS lnventorsz ErkkiTapio Tirkkonen, Helsinki;

Pekka Typpii, Hiekkaharju, both of Finland.

Assignee: Oy Nokia-Ab, Helsinki, Finland Filed: June 11, 1973 Appl. No.:369,066

Related US. Application Data Continuation-impart of Ser. No. 187,411,Oct. 7, 1971,

References Cited UNITED STATES PATENTS 1/1966 Barker, Jr. .250/3-59 X[451 Apr. 23, 1974 2,946,253 7/1960 Clark, Jr. 250/227 X PrimaryExaminerJames W. Lawrence Assistant Examiner- T. N. Grigsby Attorney,Agent, or Firm-Kurt Kelman 57 ABSTRACT Apparatus is disclosed for themeasurement of a variable parameter at different points distributedacross the width of a web of material travelling lengthwise relative tothe apparatus. The apparatus includes a first set of light tubes fixedin relation to said apparatus and extending from a light sourcetransversely of the web of material with their output ends spaced acrossthe width of the web of material. A second set of light tubes also isfixed in relation to said apparatus and extends from light sensitivemeans transversely of the web material with their input ends spacedacross the width of the web of material. The input ends are respectivelyassociated with corresponding light output ends of the light tubes ofthe first set.

7 Claims, 7 Drawing Ei gures $3 gsA llTl WW I PATENTEUAPR 23 mm SHEET 1[1F 2 PATENTED APR 2 a 1974 SHEET 2 [IF 2 VM/I Fig.7

This is a continuation-in-part of our copending U.S.

Pat. application Ser. Ne. 187,411, filed Oct. 7, 1971 pending in artunit 256.

This invention relates to an improvement in apparatus disclosed in US.Pat. application Ser. No. 135,201, now abandoned, by one of the jointinventors Erkki Tapio Tirkkonen. The apparatus is adapted for themeasurement of a variable parameter at different points distributedacross the width of the web of material travelling lengthwise relativeto the apparatus.

The continuing development of paper making machines and the increase oftheir production speeds and web widths impose the necessity ofelaborating ever faster measuring devices, by the aid of which thepapermaking is also controlled. For successful control to be possible,one has to be able to measure the base Weight and moisture content ofthe paper web with high accuracy and high speed at various points on thewire up to the take-up unit.

It is necessary to perform measurement over the entire width of thepaper web, and the accuracyof differentiation should be as high as -20mm. Moreover, it should be possible to determine the transversal profilewithin a short period, in order that the longitudinal displacement ofthe profile might be minimal. It would be advantageous, and in manyinstances indispensable, to perform the measurement without contact withthe paper web. The equipment which has to be mounted on the papermachine should have as small'weight as possible and it should take up aminimum of space.

Existing measuring devices do not meet the above requirements. This istrue even of the more sophisticated types of measuring equipmentpreviously available, while their cost is such that their use is noteconomic.

An object of the present invention is the provision of improvedmeasuring apparatus which meets the above requirements, and which isboth relatively simple in design and relatively cheap to provide.

According to the present invention, apparatus adapted for themeasurement of a variable parameter at different points distributedacross the width of a web of material travelling lengthwise relative tothe said apparatus comprises a first set of so-called lighttubes fixedin relation to said apparatus and extending from a light sourcetransversely of the web of material with their output ends spaced acrossthe width of the web of material, and a second set of so-called lighttubes also fixed in relation to said apparatus and extending from lightsensitive means transversely of the web material with their input endsspaced across the width of the web of material and respectivelyassociated with corresponding light output ends of the light tubes ofthe first set.

The invention will now be described, by way of example, with referenceto the accompanying drawings, in which:

FIG. 1 is a perspective drawing of an arrangement of light tubesaccording to the present invention;

FIG. 2 is a diagrammatic representation of the arrangement of lighttubes shown in FIG. 1;

FIGS. 3 through 6 are side elevations showing alternative endings forthe light tubes; and

FIG. 7 is an underneath view of the arrangement of light tubes of FIGS.1 and 2.

As explained in the aforesaid US. Pat. application Ser. No. l35,20l inorder that a travelling web of paper may be examined for defects, asuitable light" type of radiation is supplied to the inlet ends of anarrangement of light tubes, the output ends of which are spaced apart inthe form of a line to emit light towards the web at a large number ofspaced locations distributed across the width of the web. On the otherside or face of the web, is a similar arrangment of light tubes with theoutput ends of the first light tubes opposite the input ends of thesecond light tubes. Radiation from the first light tubes passes throughthe web and entersthe other light tubes which lead the light to asuitable detection apparatus.

Suitably the radiation used is infrared, and the light source consistsof hologen lamps of 2 kilowatt each run at reduced voltage to produce acolour temperature of 2,500K. The exact colour temperature is notcritical but should be kept above 2,10OK.

The present invention is directed to the arrangement of the light tubes,and in general a first set of light tubes 1 is arranged above the web 3of paper to be examined, and a second set of light tubes 5 is arrangedbelow the web 3. As indicated in FIG. 1, light is fed into the lefthandend of the first set 1 through an adaptor 7, and light is withdrawn fromthe righthand end of the second set 5 through an adaptor 9.

This feature has the advantage that for each combination of a light tubefrom the first set, and a light tube from the second set, the totaltransmission length can be kept the same. This feature is important inthe preferred arrangment in which infrared absorption is used to measurea parameter. Thus a stationary infrared souce 11 is situated on one sideof the web and a stationary infrared analyser 13 on the other side ofthe web.

In FIG. 2, for example, a light tube 15 of the first set 1 has itsoutlet end 15A arranged'opposite an inlet end 17A of a light tube 17 ofthe second set, and it will be seen that the total length of light tubeis the same as in the case of light tube 19 of the first set, which hasits outlet end 19A arranged opposite inlet end 21A of light tube 21 ofthe second set.

The light tubes in the preferred embodiments of the I invention shownconsist of rectangular aluminum pipes with bright inside surfaces. Aconsiderable number of light tubes is required, and the pipes formingthe tubes are bonded together by epoxy cement to form a selfsupportingbeam structure. For example, each pipe' can cover a section of 100 mm.of the width of the web, and the space between adjacent outlet ends inthe first set can be minimal so that the whole width of the web iscovered. During operation of the apparatus, the gap between the upperand lower beam is mm., but the lower set of tubes is positioned by ahydraulic device, so that the beam consisting of the lower set of tubescan be lowered as a unit to increase the spacing from the beam formed bythe upper set of light tubes to 500 mm., so facilitating threading ofthe web between the two sets of light tubes.

The interiors of the pipes forming the light tubes are filled with aninert gas, for example, argon, under a slight positive pressure. Oneresult of this is that light obscuring gases cannot enter the pipes toaffect the light transmission while the use of an inert gas reduces to aminimum oxidation of the bright inner surfaces of the light tubes.

As will be clear from FIGS. 3 through 7, there are several ways in whichthe light tubes can be formed and arranged, and the arrangement adoptedmust depend upon the number of light tubes to be used. In FIG. 7, fivelight tube unit stacks are arranged side by side, and each light tubeunit will provide three light tubes. In each stack of light tube units,the number of light tube units can be selected as desired, the resultingincrease in height of the beam increasing the stiffness of the beam andthus being an advantage rather than a disadvantage.

In the arrangement shown in FIG. 4, a group of three light tubes 41terminate at a planar mirror 43 so that each light tube delivers lightto, or receives light from, only the appropriate part of the web 3through a suitable window 45.

In the arrangement shown in FIG. 5, each light tube 51 is complete initself, and at its inlet or outlet end at the web is provided with itsown, mirror surface 53 so that the outlet ends of the light tubes aredirected at the web 3 through a suitable window 55.

- In the arrangement shown in FIG. 6, each of a group of light tubes 61terminates at a-planar mirror 63, but in this case the reverse side ofthe mirror is also a mirror surface. In this way, light from the uppertwo of the three light tubes experiences multiple reflections betweenthe light tube and the web 3, passing through a suitable window 65.

The arrangement of the light tubes in the beam 1 can be similar to thearrangement of the light .tubes in the beam 5, or somewhat differentarrangements can be used, as desired.

It will be seen that the apparatus described above makes use of arelatively cheap form of light tube; the light tubes are combined as abeam to provide a selfsupporting arrangement; and the total length ofeach transmission path between light source and analyser is either thesame or very nearly equal to that of the other transmission paths.

In the practical fabrication of the light tubes, it will be foundconvenient to provide the structure of the light tubes over the fulllength of the beam, and in each light tube insert a deflecting mirrorand a window at the appropriate points. In this way the beam will havethe general appearance indicated in FIG. 1, and will be of uniformrigidity and will be free from undesirable'external ledges andprojections. The light tubes described are so cheap to manufacture thatno serious additional expense is involved in extending them across thefull width of the web.

Since, in each beam, lighttravels along each light tube from one end andthen leaves the light tube, if desired the remaining part of the lighttube can be used for the return of light reflected from the surface ofthe web. This can be useful when the examination of the web which isrequired is to be carried out by the use of reflected light, rather thanby transmitted light.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:

1. Apparatus adapted for the measurement of a variable parameter atdifferent points distributed across the width of a web of materialtravelling lengthwise relative to the said apparatus, comprising a firstset of infrared radiation emitting tubes fixed in relation to saidapparatus and mechanically combined to form a first rigid beam extendingfrom a light source transversely across the full width of the web ofmaterial with their output ends spaced across the width of the web ofmaterial, and a second set of infrared radiation emitting tubes alsofixed in relation to said apparatus and mechanically combined to form asecond rigid beam extending from light sensitive means transverselyacross the full width of the web material with their input ends spacedacross the width of the web of material and respectively associated withcorresponding light output ends of the tubes of the first set, thelength of each tube in the first set being so related to the length ofthe associated tube in the second set that the sum of their lengths issubstantially the same for each such pair of tubes.

2. Apparatus as claimed in claim 1, wherein the first set of tubes isdisposed on one side or face of said web and the second set of tubes isdisposed on an opposite side or face of said web. I

3. Apparatus as claimed in claim 1, wherein one of these beams isdisposed above the web of material, and the other of these beams isdisposed below the web of material.

4. Apparatus as claimed in claim 1, wherein the tubes have reflectiveinner surfaces. v

5. Apparatus as claimed in claim 1, wherein the tubes are aluminum tubeshaving highly reflective inner surfaces. y 6. Apparatus as claimed inclaim 1 wherein the tubes are metal tubes having highly polished innersurfaces, and filled with an inert gas selected to inhibit deteriorationof said polished surfaces.

7. Apparatus as claimed in claim l, wherein the tubes have reflectiveinner surfaces and filled with a transparent gasunder a positivepressure, precluding the ingress of light obscuring gases.

I UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3, 0,730 Dated April 23. 1974 InVent0r(S) Ftr'kki ",apin 'I'ir'kko'n n Gt alIt is certified that error appears in the above-identified patent andthat said Letters Patent are hereby corrected as shown below:

On the title page, between items 16: 7 and A527, insert:--

597 Foreign Application Priority Data Sep. 29, 1971 Finland 2715/71Signed and sealed this 24th day of September 1974.

(SEAL) Attest:

McCOY M. GIBSON JR. C. MARSIiALL DANN Attesting Officer vCOIIITIiSSlOI'IQI of Patents :ORM po'wso v uscoMM-Dc 60376-P69 U.S.GOVERNMENT PRINTING OFFICE: I!" 0-366-334.

1. Apparatus adapted for the measurement of a variable parameter atdifferent points distributed across the width of a web of materialtravelling lengthwise relative to the said apparatus, comprising a firstset of infrared radiation emitting tubes fixed in relation to saidapparatus and mechanically combined to form a first rigid beam extendingfrom a light source transversely across the full width of the web ofmaterial with their output ends spaced across the width of the web ofmaterial, and a second set of infrared radiation emitting tubes alsofixed in relation to said apparatus and mechanically combined to form asecond rigid beam extending from light sensitive means transverselyacross the full width of the web material with their input ends spacedacross the width of the weB of material and respectively associated withcorresponding light output ends of the tubes of the first set, thelength of each tube in the first set being so related to the length ofthe associated tube in the second set that the sum of their lengths issubstantially the same for each such pair of tubes.
 2. Apparatus asclaimed in claim 1, wherein the first set of tubes is disposed on oneside or face of said web and the second set of tubes is disposed on anopposite side or face of said web.
 3. Apparatus as claimed in claim 1,wherein one of these beams is disposed above the web of material, andthe other of these beams is disposed below the web of material. 4.Apparatus as claimed in claim 1, wherein the tubes have reflective innersurfaces.
 5. Apparatus as claimed in claim 1, wherein the tubes arealuminum tubes having highly reflective inner surfaces.
 6. Apparatus asclaimed in claim 1 wherein the tubes are metal tubes having highlypolished inner surfaces, and filled with an inert gas selected toinhibit deterioration of said polished surfaces.
 7. Apparatus as climedin claim 1, wherein the tubes have reflective inner surfaces and filledwith a transparent gas under a positive pressure, precluding the ingressof light obscuring gases.